There's often talk here on the forum about replacing power cords on kilns. This may be because the prongs on the cord don't match the outlet, or a longer cord is needed. It seems like a simple thing, but there are a few things you need to look for:
1. If it's a new kiln, replacing the cord on a new kiln may void the warranty unless it's done by an approved technician or with a cord from the manufacturer. True, it would be tough for them to ever find out, but it could happen if you need a tech in the future, and karma can be a real bugger. Plus it's usually easier to replace the wall outlet than change the cord. Also, changing the power cord to one with a different plug configuration or length length may void the UL listing (if the kiln has one), which may affect how your insurance company feels about the kiln. In all cases, you should check with the manufacturer first before making changes.
2. Make sure the new cord is rated for the same amperage as the old cord. Too small and you'll have a major safety issue on your hands.
3. Make sure it has the same number of prongs. Single phase kilns usually have 3 prongs- two hots and a ground. 3 phase kilns have 4 prongs- 3 hots and a ground. Some single phase kilns also have 4 prongs- 2 hots, a neutral and a ground. You cannot change this! Never snap off a grounding prong! It is very dangerous to fire a kiln that is not grounded.
4. Make sure the cord is rated for 105C/220F. This is the one that everyone overlooks. Most power cords you can get at the hardware store are only rated for 90C, which could overheat.
5. Wire it up properly. That means putting the hots, ground and neutral in the right places, as well as using the proper strain relief to hold the cord tight in the control box. Make sure all the connections are good and tight!
6. Building your own cord is often the best way to go, especially if you need a longer than normal cord. SEOOW type cords are wonderfully flexible and easy to work with. They can be purchased online from McMaster Carr or other sellers. You just have to attach the appropriate plug to the cord, which isn't all that difficult. I have found that plugs from McMaster are pretty pricey, so I usually get the plug from Ace, Lowes, etc. If ring terminals are required for the kiln connection, I recommend using high temp terminals. If the old wires have heat resistant sleeves on them, you can reuse them on the new cord if they're in good condition. Otherwise get new sleeves.